Method for forming transparent thin film, transparent thin film formed by the method, and transparent substrate with transparent thin film

ABSTRACT

The present invention provides a method for forming a transparent thin film by a chemical vapor deposition method using a gaseous raw material. In the method, a film growth rate is at least 8 nm/s, and the transparent thin film contains at least one selected from carbon (C) and oxygen (O), nitrogen (N), hydrogen (H), and silicon (Si). According to this method, a transparent thin film that does not peel off a substrate easily due to the eased tension in the thin film and has high transmittance in the visible light region can be deposited on a glass ribbon in a float bath.

TECHNICAL FIELD

The present invention relates to a method for forming a thin film thatcontains silicon nitride (SiN) as its basic framework and, for example,carbon present therein and has a high visible-light transmittance.Furthermore, the present invention relates to a transparent substratewith a transparent thin film formed by the method, which is atransparent substrate with a transparent thin film that is suitable foruses such as, for example, buildings, vehicles, or displays.

BACKGROUND ART

A technique of forming a thin film on a glass substrate using a chemicalvapor deposition method (hereinafter referred to as a “CVD method”) iswell known. The thin films to be formed are of various kinds and one ofthem is a silicon nitride (SiN) film. The silicon nitride thin film hasbeen used widely as an insulating film in the field of semiconductors.In addition, since the silicon nitride thin film has a dense structure,it also is used as a barrier to the diffusion of various ions such assodium, silver, etc., for example, as an acid-proof mask. A glasssubstrate with a silicon nitride thin film has high transmittance in thevisible light region and thus is suitable for use for buildings,vehicles, or display substrates.

As a method for forming a silicon nitride thin film is known a method ofdepositing a film by an atmospheric CVD method using monosilane (SiH₄)and ammonia (NH₃). In the conventional film depositing method, however,the concentration of monosilane contained in a gaseous raw material wasrelatively low, for example, 0.1 mol % or lower. The silicon nitridethin film has high tension therein and may peel off a glass substrate insome cases, which has been a problem. As a means for solving thisproblem is known a technique of reducing the tension by including oxygenin a thin film to form a silicon oxynitride (SiON) film. For example,JP10(1998)-309777A discloses a technique of depositing a thin filmcontaining silicon nitride and silicon oxynitride as its main componentson the surface of a glass substrate by the CVD method.

Furthermore, for instance, JP2001-100811A discloses a method that takesinto consideration the passivation function of a silicon nitride thinfilm, in order to form a perfect silicon nitride thin film, i.e. asilicon nitride thin film containing no impurities, and the flow ratio(SiH₄/NH₃) between monosilane and ammonia contained in the gaseous rawmaterial is set at a low ratio, particularly, about 0.086 in aplasma-enhanced CVD method.

However, the film growth rate of silicon nitride and silicon oxynitrideby the conventional CVD method is low, particularly about a few nm/salthough it also depends on the film forming apparatus. In particular,when the above-mentioned thin film is deposited on the surface of aglass ribbon which floats on molten tin in a float bath in the processof producing float glass by the CVD method (hereinafter, this formationmethod is referred to as an “on-line CVD method”), it was difficult forthe thin film to grow up to a thickness enough for its characteristicsto be exhibited fully at a conventional film growth rate. In the on-lineCVD method, it is conceived that when a thin film containing siliconnitride and silicon oxynitride as its main components is formed, a filmgrowth rate of at least about 8 nm/s is required to make the thin filmgrow so that it has a thickness allowing its characteristics to beexhibited fully, although it also depends on the moving rate of theglass ribbon.

DISCLOSURE OF THE INVENTION

The present invention was made with the aforementioned problems in mind.The present invention is intended to provide a method for forming atransparent thin film that does not peel off a substrate easily due tothe eased tension in the thin film and has high transmittance in thevisible light region, at a high film growth rate that can be employed inan on-line CVD method. Furthermore, the present invention is intended toprovide a transparent substrate with a transparent thin film obtained bythe method, which is suitable for uses such as buildings, vehicles,displays, etc.

In order to achieve the above-mentioned objects, the present inventionprovides a method for forming a transparent thin film by a CVD methodusing a gaseous raw material, wherein the transparent thin film thatcontains at least one selected from carbon (C) and oxygen (O), nitrogen(N), hydrogen (H), and silicon (Si) is formed at a film growth rate ofnot less than 8 nm/s.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of a transparentsubstrate with a transparent thin film according to the presentinvention.

FIG. 2 is a schematic view of an appratus used in an on-line CVD method.

FIG. 3 is a cross-sectional view of an embodiment of a transparentsubstrate with a transparent thin film and a functional thin filmstacked thereon.

EMBODIMENTS OF THE INVENTION

In the formation method of the present invention, it is preferable thatthe gaseous raw material contains at least 0.2 mol % of asilicon-containing compound.

Preferably, the gaseous raw material contains a silicon-containingcompound and ammonia. The mole ratio of the ammonia to thesilicon-containing compound in the gaseous raw material may be set at,for example, 40 to 400.

It is preferable that the gaseous raw material contains monosilane(SiH₄) as a silicon-containing compound.

It also is preferable that the gaseous raw material is blown onto thesurface of a glass ribbon in a float bath, although it may be blown ontoa pre-cut glass sheet. A suitable surface temperature of the glassribbon is, for example, 700° C. to 830° C. The glass ribbon may have athickness of 4 mm or less, or a line speed of the glass ribbon may be asfast as the speed that allows the glass ribbon to be formed to have athickness of 4 mm or less.

From another aspect, the present invention provides a transparent thinfilm formed by the method according to the present invention, wherein anatomic percentage of hydrogen content is 4 to 20 atom %, preferably 5 to20 atom %. This transparent thin film can have a thickness of at least40 nm while having a visible light transmittance of at least 83%.

From a further aspect, the present invention provides a transparentsubstrate with a transparent thin film, wherein the transparent thinfilm is formed on the surface of the substrate and is theabove-mentioned transparent thin film of the present invention. It ispreferable that the transparent substrate is a glass sheet. Thetransparent substrate with a transparent thin film further may include afunctional thin film formed on the surface of the transparent thin film.

Hereinafter, a preferred embodiment of the present invention isdescribed further with reference to the drawings.

FIG. 1 shows a transparent substrate, for example, a glass substrate 1,that is covered with a transparent thin film 2 containing carbon and/oroxygen, nitrogen, hydrogen, and silicon as main components. The thinfilm 2 may be formed using a so-called physical vapor deposition methodsuch as a sputtering method, an ion-plating method, a vacuum depositionmethod, or the like. In the present invention, however, a CVD method isemployed. The physical vapor deposition method is excellent inuniformity of film thickness, but when consideration is given to, forexample, durability of the thin film obtained after its formation, thefilm formation by the CVD method is preferable. Among the CVD methods,particularly an atmospheric thermal CVD is suitable. In some cases, acatalytic CVD method may be used in which a contact decompositionreaction of a gaseous raw material with a catalyst placed in thevicinity of the transparent substrate is utilized. The deposition of thethin film by the CVD method can be carried out through blowing of agaseous raw material on a transparent substrate that has been cut into apredetermined size and has been heated. For instance, while a glasssheet is placed on a mesh belt and is conveyed through a heatingfurnace, a gaseous raw material is supplied to react at the surface ofthe glass substrate heated to a predetermined temperature.

It is preferable that the gaseous raw material for the transparent thinfilm contains at least a silicon-containing compound and ammonia. Inthis connection, examples of the silicon-containing compound include notonly silicon hydride expressed as Si_(n)H_(2n+2) but also an organicsilicon compound. Besides silicon hydrides such as monosilane (SiH₄),disilane (Si₂H₆), for example, silicon hydrides in which at least a partof hydrogen is substituted with a halogen, such as silicon tetrachloride(SiCl₄), dichlorosilane (SiH₂Cl₂), silane trichloride (SiHCl₃), silicontetrafluoride (SiF₄), etc., silane containing an alkyl group, such astetramethylsilane ((CH₃)₄Si), etc. can be used. It is preferable thatamong them, monosilane is used. Since monosilane is easily reacts withammonia, less by-products are produced during the film deposition andthe content ratio of carbon, oxygen, and hydrogen in the transparentthin film can be adjusted in a broad range.

Ammonia is a nitrogen raw material that has been used conventionally ina CVD method, and is readily available and inexpensive. Conventionally,nitrogen, amines, hydrazine-type organic compounds, etc. also have beenused as nitrogen raw materials. Nitrogen, however, is poor inreactivity. Moreover, organic compounds are difficult to be supplied asraw materials on an industrial production scale, and their toxicitybecomes a problem when they are used on a production scale. The use ofammonia in a gaseous raw material can prevent carbon from beingcontained in the transparent thin film and thereby can improve the filmgrowth rate.

It is preferable that the film growth rate of the transparent thin filmis as high as possible for industrial production. For instance, in anexample described in JP10(1998)-309777A, it is described that a siliconnitride thin film was deposited at a film growth rate of 60 nm/min=1nm/s using silane and ethylamine as raw materials. In the presentinvention, compared with that disclosure, the film growth rate can beimproved to 8 nm/s or higher by using a gaseous raw material containing,for example, silicon hydride and ammonia. In actual production, however,the uniformity of the transparent thin film tends to deteriorate withthe increase in the film growth rate, and for example, its thickness mayvary several-fold from portion to portion or defects such as pinholesmay be caused. Hence, the film growth rate naturally has itslimitations. Even in the on-line CVD method in which a higher filmgrowth rate is required, if a film growth rate is 15 nm/s, a transparentthin film with a sufficient thickness substantially can be formed on aglass ribbon for one millimeter glass sheet for the production of whicha higher rate speed is required. It therefore is preferable that a filmgrowth rate of 8 to 15 nm/s is set as a target speed.

Preferably, the concentration of the silicon-containing compound in thegaseous raw material is at least 0.2 mol %. If this concentration isless than 0.2 mol %, the film growth rate may decrease to lower than 8nm/s even when the surface temperature of the transparent substrate is800° C. or more. Accordingly, it takes an excessively long time to formthe film. Particularly, in an on-line CVD method, a film growth rate oflower than 8 nm/s causes a problem in that the thickness of a usableglass ribbon is limited to a range exceeding approximately 4 mm,although it also depends on the film depositing apparatus and operatingconditions. On the other hand, when the concentration of thesilicon-containing compound is excessively high, it becomes difficult tokeep its mole ratio to ammonia within the above-mentioned range. Hence,an adequate upper limit of the concentration of the silicon-containingcompound is 2.4 mol % in the CVD method. Furthermore, when theconcentration of the silicon-containing compound is excessively high,not only does a thermal decomposition reaction proceed in a vapor phaseto change it into a powdery state, which causes defects such as pinholesin the transparent thin film and decreases the film growth rate, butalso there is a danger of explosion of the silicon-containing compoundin the gaseous raw material. It therefore is practical to set theconcentration of the silicon-containing compound at 1.4 mol % or lower.

Preferably, the mole ratio of ammonia to the silicon-containing compoundin the gaseous raw material (the number of moles of ammonia/the numberof moles of the silicon-containing compound) is 40 to 400. When the moleratio is smaller than 40, a large number of Si—Si bonds are formed andthereby a thin film is formed that has its absorption band in thevisible light region and thus has low transparency. On the other hand,when the mole ratio exceeds 400, not only it is difficult to increasethe concentration of the silicon-containing compound in the gaseous rawmaterial, but also ammonia inhibits the silicon-containing compound frombeing decomposed, which results in a decrease in the film growth rate.In this connection, with respect to the mole ratio of ammonia to thesilicon-containing component, the ratio of ammonia is several times ashigh as that employed in the conventional method described in, forexample, JP2000-100811A.

Oxygen to be provided in the transparent thin film is supplied fromoxidizing raw materials such as, for example, dinitrogen monoxide,carbon monoxide, and carbon dioxide that are added to the gaseous rawmaterial. Even when these oxidizing raw materials are not added to thegaseous raw material, oxygen may be provided in the vicinity of thesurface of the transparent thin film through natural oxidation caused bythe contact with the atmosphere after the film is formed. The carbon tobe provided in the transparent thin film may be a residue of the organicsilicon compound or may be supplied from lower hydrocarbon such asacetylene, ethylene, ethane, or the like that is added to the gaseousraw material to control the reactivity of the silicon-containingcompound having high reactivity such as monosilane. The hydrogen to beprovided in the transparent thin film is a residue of asilicon-containing compound containing hydrogen such as silane or thelike, or ammonia. It is presumed that with these elements provided inthe basic framework of silicon nitride, the nitrogen-silicon bond is cutat some sites, the tension of the transparent thin film is easedaccordingly, and thus the transparent thin film does not peel off thetransparent substrate easily.

To the gaseous raw material may be added nitrogen, helium, hydrogen, orthe like in addition to the above-mentioned silicon-containing compound,ammonia, an oxidizing raw material, and lower hydrocarbon.

The transparent substrate on which the transparent thin film is formedis not particularly limited as long as it has corrosion resistance andthermal resistance to withstand the film formation performed by the CVDmethod and can be used for the above-mentioned uses such as windows ofbuildings or the like. Examples of the transparent substrate may includea glass sheet, a heat resistant resin, and the like.

When a glass sheet is used as the transparent substrate, a transparentthin film may be formed on the glass sheet that has been cut into asuitable size or may be formed at the same time the glass sheet isformed by the on-line CVD method, which is described later. In theindustrial production, the latter in which the on-line CVD method isemployed has more advantages. In the on-line CVD method, since a film isdeposited on the surface of a glass ribbon having a heat that is higherthan its softening point in a float bath, the heat of the glass ribbonpromotes the thermal decomposition reaction of the gaseous raw material.As a result, heating required for the thermal decomposition reaction isno longer necessary, and thereby the total energy cost is reduced.Furthermore, the film growth rate and the film growth efficiency areimproved, which prevents the defects such as pinholes from being caused.Moreover, when using the on-line CVD method, since the glass ribbonheated to a point higher than its softening point has some changeabilityin its surface form, the tension inside the film that is peculiar to thesilicon-nitride-based thin film is reduced and thus a transparent thinfilm is formed that has high adhesiveness and high mechanical strength.

In the CVD method, the film growth rate further can be improved byspraying ammonia on the surface of the glass substrate or glass ribbonimmediately before the deposition of a transparent thin film.Conceivably, this is because the ammonia that has come into contact withthe glass substrate or glass ribbon is decomposed, and then adheresthereto, and thereby the thermal decomposition reaction proceeds rapidlyat the time the silicon-containing compound is supplied. Furthermore, inorder to promote the decomposition of ammonia, a catalyst may be placedin the vicinity of the surface of the glass substrate or glass ribbon.

In the on-line CVD method, the apparatus shown in FIG. 2 is used. Inthis apparatus, a glass ribbon 10 is formed from molten glass, which ispoured from a melting furnace (a float furnace) 11 into a float bath 12,and is in a belt-like form on a tin bath 15 while moving in the floatbath 12. A predetermined number of coaters 16 (three coaters 16 a, 16 band 16 c in the embodiment shown in the figure) are placed inside thefloat bath at a predetermined distance from the surface of the glassribbon 10. These coaters supply gaseous raw materials to form thin filmson the glass ribbon 10 continuously. When a plurality of coaters areused, films can be stacked on the glass ribbon 10. The temperature ofthe glass ribbon is adjusted by a heater and a cooler (not shown in thefigure) placed in the float bath so that the glass ribbon has apredetermined temperature directly before reaching the coaters 16. Theglass ribbon 10 on which the respective films have been formed is liftedby a roller 17 and then is carried into an annealing furnace 13. Theglass sheet annealed in the annealing furnace 13 is cut into a glasssheet with a predetermined size by a cutting device, which generally isused in the float glass process and is not shown in the figure.

Since the films are deposited in an upstream section inside the floatbath, the thermal diffusion of tin (diffusion of tin vapor) into thesurface (the upper face of the glass ribbon; the top surface) that isnot in contact with the molten tin can be minimized. In the case where alarge amount of tin diffuses into the upper surface of the glass ribbon,a passivation function tends to be deficient when the transparent thinfilm is relatively thin. For instance, in the case where a pastecontaining silver as its main component is applied onto the transparentthin film, which then is baked to form an electrode, if silver or tinpasses through the transparent thin film, the silver and the tin reactwith each other to cause coloring, which often becomes a problem when itis used for a display. That is, the transparent thin film is formed inthe upstream section inside the float bath, so that the problem causedby the passage of silver or tin can be solved without increasing thethickness of the transparent thin film.

In the on-line CVD method, generally, a film can be deposited on a glassribbon having a surface temperature in the range of 500° C. to 850° C.This transparent thin film preferably is deposited on the glass ribbonhaving a surface temperature in the range of 700° C. to 830° C.immediately before its deposition. This is because when the surfacetemperature is in this range, the film growth rate is high and thetension in the thin film that is peculiar to the silicon nitride film isreduced due to the changeability of surface form of the glass ribbon,and thus a transparent thin film is formed that has an improvedadhesiveness and high mechanical strength.

Since this transparent thin film contains silicon nitride as its basicframework, it has hardness, high transparency, and low absorptivity inthe visible light region. Preferably, the atomic percentages of siliconand nitrogen in the transparent thin film are 35 to 45 atom % and 30 to60 atom %, respectively. When the atomic percentage of silicon is lowerthan 35 atom %, the transparent thin film has deteriorated denseness andthereby the function providing a barrier to the diffusion of variousions is deteriorated. On the other hand, when the atomic percentage ofsilicon in the transparent thin film exceeds 45 atom %, the absorptivityin the visible light region increases and thereby the transparency ofthe thin film decreases. Furthermore, a preferable ratio of the atomicpercentage of nitrogen to the atomic percentage of silicon in thetransparent thin film is one that is as close to 1.3 as possible, whichis the stoichiometric composition ratio of silicon nitride. When theratio of the atomic percentage of nitrogen to the atomic percentage ofsilicon in the transparent thin film is lower than 0.9, the absorptionin the visible light region increases and thereby the transparency ofthe thin film decreases. Accordingly, it is suitable to adjust the ratioof the atomic percentage of nitrogen to the atomic percentage of siliconin the transparent thin film within the range of 0.9 to 1.3.

It is preferable that the transparent thin film contains 1 to 10 atom %of at least one of carbon and oxygen. Carbon changes the absorptivity inthe visible light region of the transparent thin film corresponding toits rate. On the other hand, oxygen eases the tension of the transparentthin film to reduce stress and thereby improves the adhesiveness to thetransparent substrate as well as the mechanical strength. In order toallow these functions to be exhibited efficiently, it is preferable thatthe atomic percentage of carbon and oxygen is set within the range of 1to 10 atom %. In this connection, either carbon or oxygen may becontained selectively or both may be contained. Furthermore, thistransparent thin film contains hydrogen as its essential element. Withthe increase in rate of hydrogen content, the denseness of thetransparent thin film deteriorates and accordingly the function ofproviding a barrier to the diffusion of various ions deteriorates.Hence, it is preferable that the rate of hydrogen content is 4 to 20atom %.

The preferable thickness of the transparent thin film is at least 20 nmto secure the passivation function but not more than 300 nm to securehigh visible-light transmittance. Moreover, since the reflectanceincreases with the increase in difference in refractive index betweenthe transparent thin film and a transparent electroconductive filmdescribed later or the transparent substrate, a preferable refractiveindex of the transparent thin film is 1.8 to 2.1, which is relativelyclose to the refractive indices of a glass substrate and a transparentelectroconductive film made of common tin oxide.

It is preferable that the transparent thin film has transmittance ashigh as possible. This transparent thin film can secure a visible-lighttransmittance of 83% even when having a thickness of 40 nm.

FIG. 3 shows an example of a glass substrate with a thin film 3 stackedon a transparent thin film 2. The thin film 3 contains, as its maincomponent, tin oxide (SnO₂), silicon dioxide (SiO₂), tin silicon oxide(SnSiO), silicon oxycarbide (SiOC), silicon carbide (SiC), or titaniumdioxide (TiO₂). The thin film 3 is a functional thin film. A thin filmcontaining tin oxide as its main component can function as a transparentelectroconductive film. A thin film containing silicon dioxide and tinsilicon oxide as its main component can function as a passivation filmor an insulating film. A thin film containing silicon carbide as itsmain component can function as a passivation film, an insulating film,or a brown-colored film. A thin film containing titanium dioxide as itsmain component can function as a heat reflecting film or a film having aphotocatalytic function. The combination of such a functional thin film3 with the thin film 2 allows the reflectance, electroconductivity,passivation function, or the like to be adjusted suitably and thedurability to be improved without impairing various functions of thetransparent thin film.

In FIG. 3, the thin film 2 is formed on the surface of the glasssubstrate and the functional thin film 3 is formed thereon. However, theorder and the number of films stacked on the glass substrate are notparticularly limited and can be changed suitably according to theintended use and function. For instance, in the case of theconfiguration shown in FIG. 3, since the transparent thin film 2 withhigh chemical stability and high physical strength is covered with thefunctional thin film 3, a functional glass substrate with higherdurability can be obtained.

The transparent thin film may have a composition that is substantiallyuniform in the direction of its depth, i.e. its film thickness or mayhave a composition gradient. Particularly, in the functional thin film,the composition near the interface between the functional thin film andthe transparent thin film that is in contact therewith can be varied.This can improve, for example, the adherence between the transparentthin film and the functional thin film.

The glass substrate provided with this transparent thin film fullysatisfies the characteristics required when used for buildings orvehicles. In particular, since silver-coloring does not occur in theglass substrate, it also can be used for displays, particularly for aplasma display panel substrate having stringent requirements.

In the present invention, the “main component(s)” denotes a component orcomponents accounting for at least 50 wt. % of the whole components interms of a weight ratio of its content, as it usually means.

EXAMPLES

Hereinafter, the present invention is described by means of examples butis not limited to the following examples.

Example 1

Low alkaline glass was produced by a float glass process, had athickness of 1.1 mm, and had been cut into a square whose each side was10 cm. The low alkaline glass thus produced was washed and then wasdried. A transparent thin film containing silicon nitride as its maincomponent was deposited on the glass sheet by the atmospheric CVDmethod. The film deposition was carried out under the condition that theglass sheet was conveyed in a furnace having a temperature of about 830°C. at a speed of 1.5 m/min. A gaseous raw material was supplied from acoater placed in the furnace to deposit a 40-nm thick transparent thinfilm containing silicon nitride as its main component on the surface ofthe glass substrate. In the gaseous raw material, the mole ratio ofammonia to monosilane was 200, the concentration of monosilane was 0.5mol %, and nitrogen was contained as a carrier gas. In this case, thefilm growth rate was 10 nm/s.

It was confirmed by the X-ray photo-emission spectrometry and Rutherfordbackscattering spectrometry that the composition of the transparent thinfilm included 40 atom % of silicon, 43 atom % of nitrogen, 2 atom % ofoxygen, and 15 atom % of hydrogen. The transparent thin film had avisible-light transmittance of 88.7% that was measured using aspectrophotometer, and a refractive index at 550 nm of 1.90 that wasmeasured using an ellipsometer. These characteristics are at a levelthat causes no practical problems when it is used not only for buildingsor vehicles but also for displays that require high transparency,particularly, substrates for plasma display panels that have stringentrequirements. Moreover, the transparent thin film had a surfaceresistivity of at least 10¹⁰ Ω/□(square) and thus had a high insulationability.

Furthermore, in order to check the passivation function of thistransparent thin film, a silver paste was coated on the transparent thinfilm, which was baked at 500° C. for one hour. As a result, nosilver-coloring (yellowing) was found. Since the low alkaline glass wasproduced by the float glass process, it can be judged whether tin istransmitted through the transparent thin film, based on whether thesilver-coloring was caused or not. That is, the transparent thin filmcan be said to have a sufficient passivation function that is requiredwhen it is used for a display.

The conditions of film deposition and the characteristics of thetransparent thin film are indicated together in Table 1 and Table 2.

Example 2

A thin film containing silicon nitride as its basic framework wasdeposited on the surface of a glass ribbon by the on-line CVD methodusing the apparatus shown in FIG. 2. A melted glass material having acommon soda-lime silica glass composition and a temperature of 1500° C.to 1600° C. was poured into a float bath. At the time the glass ribbonhad a temperature of 830° C., a gaseous raw material was supplied from afirst coater (16 a indicated in FIG. 3) located on the furthest upstreamside to form a 45-nm thick transparent thin film on the surface of theglass ribbon having a thickness of 2.8 mm. In the gaseous raw material,the mole ratio of ammonia to monosilane was 100, the concentration ofmonosilane was 0.4 mol %, and nitrogen was contained as carrier gas. Inthis case, the film growth rate was 9 nm/s. This glass ribbon wasannealed in an annealing furnace, which then was cut into apredetermined size by a cutting device placed further downstream. Thus,a glass substrate was produced.

With respect to this transparent thin film, its characteristics wereexamined by the same means as in Example 1. As a result, the compositionof the transparent thin film included 44 atom % of silicon, 41 atom % ofnitrogen, 2 atom % of oxygen, and 13 atom % of hydrogen. The transparentthin film had a visible-light transmittance of 85.1%, a refractive indexof 1.97, and a surface resistivity of at least 10¹⁰ Ω/□(square).Moreover, no silver-coloring was observed.

The conditions of film deposition and the characteristics of thetransparent thin film are indicated together in Table 1 and Table 2.

Comparative Example 1

A thin film was formed as in Example 2 except that a gaseous rawmaterial was used in which the mole ratio of ammonia to monosilane was450 and the concentration of monosilane was 0.15 mol %. In this case,the film growth rate was 3 nm/s, and the thin film had a thickness of 15nm. With respect to this thin film, its characteristics were examined bythe same means as in Example 1. As a result, the composition of the thinfilm included 36 atom % of silicon, 40 atom % of nitrogen, 2 atom % ofoxygen, and 22 atom % of hydrogen. The thin film had a visible-lighttransmittance of 89.5%, a refractive index of 1.85, and a surfaceresistivity of at least 10¹⁰ Ω/□(square). In addition, its transparencywas high, but silver-coloring was observed. Hence, the thin film has apoor passivation function, and thus it can be said that the thin filmcannot be used for displays that require high transparency.

The conditions of film deposition and the characteristics of the thinfilm are indicated together in Table 1 and Table 2.

Comparative Example 2

A thin film was deposited as in Example 2 except that a gaseous rawmaterial was used in which ethylamine was used instead of ammonia, themole ratio of ethylamine to monosilane was 25, the concentration ofmonosilane was 0.5 mol %, the film growth rate was 1 nm/s, and the thinfilm had a thickness of 4 nm. With respect to this thin film, itscharacteristics were examined by the same means as in Example 1. As aresult, the composition of the thin film included 33 atom % of silicon,31 atom % of nitrogen, 16 atom % of oxygen, and 21 atom % of carbon. Thevisible-light transmittance and refractive index of the thin film werenot measured. However, as long as it was observed visually, itsappearance had transparency that is comparable to that of thetransparent thin film obtained in Example 1. In the thin film, thesurface resistivity was at least 10¹⁰ Ω/□(square), but silver-coloringwas observed. Hence, it can be understood that the thin film has a poorpassivation function.

The conditions of film deposition and the characteristics of the thinfilm are indicated together in Table 1 and Table 2.

TABLE 1 Conditions of Film Deposition Concen- Temper- Film NH₃/SiH₄tration ature of Growth Composition of Thin Film (Mole of Silane GlassRate (atom %) Ratio) (mol %) (° C.) (nm/s) Si N O H C Example 1 200 0.5830 10 40 43 2 15 0 Example 2 100 0.4 830 9 44 41 2 13 0 Comparative 4500.15 830 3 36 40 2 22 0 Example 1 Comparative  25*¹⁾ 0.5 830 1 33 31 160 21 Example 2 *¹⁾Ethylamine was used instead of ammonia.

TABLE 2 Characteristics of Thin Film Film Trans- Surface Coloring dueThickness mittance Refractive Resistivity to Heat (nm) (%) Index (

/□) Treatment Example 1 40 88.7 1.9 ≧10¹⁰ None Example 2 45 85.1 1.97≧10¹⁰ None Compar- 15 89.5 1.85 ≧10¹⁰ Yellow ative Example 1 Compar- 4Not Not ≧10¹⁰ Yellow ative Measured Measured Example 2

Through the comparison made between the examples and the comparativeexamples, it can be understood that the composition of the transparentthin film can be adjusted by varying the concentrations of silane andammonia contained in the gaseous raw material used in the CVD method. Inaddition, it can be understood that the transparent thin film depositedunder the film deposition conditions of the present invention has highvisible-light transmittance, high insulation ability, and an excellentpassivation function.

Specifically, through the comparison made between Examples 1 and 2 andComparative Example 1, it is understood that the rate of silicon contentin the thin film to be formed decreases with increase in mole ratio ofammonia to monosilane in the gaseous raw material. Furthermore, it alsocan be understood that with increase in the rate of silicon content, thevisible-light transmittance of the thin film decreases and itsrefractive index increases.

With the above-mentioned configurations, the present invention providesthe following effects. According to the method for depositing atransparent thin film of the present invention, a film growth rate canbe achieved that is sufficiently high to allow the rate to be used inthe on-line CVD method. By suitably maintaining the concentration of asilicon-containing compound and suitably adjusting the rate of ammoniacontent to the silicon-containing compound content in the gaseous rawmaterial, a transparent thin film that has high transparency and doesnot peel off the transparent substrate easily can be deposited reliablywhile the film growth rate is kept high.

By using the film forming method of the present invention in the on-lineCVD method, a transparent thin film with a large area having no defectssuch as pinholes can be formed in short time. Furthermore, in theon-line CVD method, since the energy required for the thermaldecomposition reaction of the gaseous raw material is obtained from aglass ribbon, the total energy cost of the glass substrate with atransparent thin film can be reduced.

The glass substrate with a transparent thin film according to thepresent invention fully satisfies the characteristics required when itis used for buildings or vehicles. Especially, since no silver-coloringoccurs, it is suitable for displays, particularly as substrates forplasma display panels having stringent requirements.

1. A transparent thin film comprising nitrogen (N), hydrogen (H), andsilicon (Si), and at least one selected from carbon (C) and oxygen (O),wherein an atomic percentage of hydrogen is 4 to 20 atom %, an atomicpercentage of silicon is 35 to 45 atom %, and an atomic percentage ofnitrogen is 30 to 60 atom %.
 2. The transparent thin film according toclaim 1, wherein the refractive index of the transparent thin film is1.8 to 2.1.
 3. The transparent thin film according to claim 1, whereinthe film is formed by a chemical vapor deposition method using a gaseousraw material and the film is formed at a film growth rate of not lessthan 8 nm/s.
 4. The transparent thin film according to claim 1, whereinthe transparent thin film has a thickness of at least 40 nm and avisible-light transmittance of at least 83%.
 5. A transparent substratewith a transparent thin film, comprising a transparent substrate and atransparent thin film formed on a surface of the transparent substrate,wherein the transparent thin film is a transparent thin film accordingto claim
 1. 6. The transparent substrate with a transparent thin filmaccording to claim 5, wherein the transparent substrate is a glasssheet.
 7. The transparent substrate with a transparent thin filmaccording to claim 5, further comprising a functional thin film formedon a surface of the transparent thin film.
 8. A transparent thin filmcomprising nitrogen (N), hydrogen (H), and silicon (Si), and at leastone selected from carbon (C) and oxygen (O), wherein an atomicpercentage of hydrogen is 4 to 20 atom %, and an atomic percentage ofcarbon and oxygen is 1 to 10 atom %.
 9. The transparent thin filmaccording to claim 8, wherein the refractive index of the transparentthin film is 1.8 to 2.1.
 10. The transparent thin film according toclaim 8, wherein the film is formed by a chemical vapor depositionmethod using a gaseous raw material and the film is formed at a filmgrowth rate of not less than 8 nm/s.
 11. The transparent thin filmaccording to claim 8, wherein the transparent thin film has a thicknessof at least 40 nm and a visible-light transmittance of at least 83%. 12.A transparent substrate with a transparent thin film, comprising atransparent substrate and a transparent thin film formed on a surface ofthe transparent substrate, wherein the transparent thin film is atransparent thin film according to claim
 8. 13. The transparentsubstrate with a transparent thin film according to claim 12, whereinthe transparent substrate is a glass sheet.
 14. The transparentsubstrate with a transparent thin film according to claim 12, furthercomprising a functional thin film formed on a surface of the transparentthin film.
 15. A transparent thin film comprising nitrogen (N), hydrogen(H), and silicon (Si), and at least one selected from carbon (C) andoxygen (O), wherein an atomic percentage of hydrogen is 4 to 20 atom %,and the ratio of the atomic percentage of nitrogen to the atomicpercentage of silicon is 0.9 to 1.3.
 16. The transparent thin filmaccording to claim 15, wherein the refractive index of the transparentthin film is 1.8 to 2.1.
 17. The transparent thin film according toclaim 15, wherein the film is formed by a chemical vapor depositionmethod using a gaseous raw material and the film is formed at a filmgrowth rate of not less than 8 nm/s.
 18. The transparent thin filmaccording to claim 15, wherein the transparent thin film has a thicknessof at least 40 nm and a visible-light transmittance of at least 83%. 19.A transparent substrate with a transparent thin film, comprising atransparent substrate and a transparent thin film formed on a surface ofthe transparent substrate, wherein the transparent thin film is atransparent thin film according to claim
 15. 20. The transparentsubstrate with a transparent thin film according to claim 19, whereinthe transparent substrate is a glass sheet.
 21. The transparentsubstrate with a transparent thin film according to claim 19, furthercomprising a functional thin film formed on a surface of the transparentthin film.